Prognostic value of cycle exercise testing prior to and after outpatient cardiac rehabilitation

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Abstract

Background

The prognostic value of cycle exercise testing prior to and after outpatient cardiac rehabilitation (OCR) is not well established.

Methods

2146 consecutive patients undergoing symptom-limited cycle exercise testing at OCR entry, of whom 1853 (86%) also had a test at end of OCR, were followed for a median of 33 months.

Results

All-cause and cardiovascular annual mortality rates were 1.2% and 0.8%, respectively. At OCR entry, older age, diabetes, lower left ventricular ejection fraction (LVEF), calcium channel blocker use, and lower workload [hazard ratio (HR) 2.38 if ≤ 105 W; p < 0.001] were independent predictors of death. Diabetes, diuretic use, and lower workload [HR 3.53 if ≤ 105 W; p = 0.001] were independently associated with cardiovascular death. At end of OCR, older age, lower LVEF, lower workload (HR 2.34 if < 140 W; p = 0.009), and lower increase in peak heart rate from entry to end of OCR (HR 2.46 if < 4 bpm; p = 0.002) were independently associated with all-cause mortality. Older age, lower LVEF, lower increase in systolic blood pressure (HR 2.97 if < 54 mm Hg; p = 0.02), and lower increase in peak heart from entry to end of OCR (HR 2.72 if < 4 bpm; p = 0.013) were independently associated with cardiovascular mortality. Failure to undergo a test at end of OCR was an additional independent predictor of all-cause (HR 2.51; p < 0.001) and cardiovascular mortality (HR 2.56; p = 0.003).

Conclusion

Symptom-limited cycle exercise testing prior to and after OCR provides important prognostic information.

Introduction

Participation in cardiac rehabilitation programs improves both mortality and morbidity outcomes in patients with coronary artery disease (CAD) [1], [2]. To optimize the training effect, a baseline exercise test for an assessment of functional capacity and development of an appropriate training description has been recommended for all CAD patients entering a rehabilitation program [3]. Interestingly, exercise capacity assessed by direct measurement of peak oxygen consumption (peak VO2) prior to the rehabilitation not only serves to tailor the training program but also is the most important predictor of cardiac and all-cause mortality in these patients [4], [5]. Peak VO2 at rehabilitation entry seems to have similar prognostic value as in other settings [6], [7], although peak VO2 at this stage is often significantly impaired due to de-conditioning after a cardiac event or cardiac surgery, and markedly improves within a few weeks during the subsequent rehabilitation program [8]. In practice however, peak VO2 prior to the rehabilitation program is often not directly measured but estimated based on the maximal external workload achieved [3], [8]. This practice may be associated with significant inaccuracy, in particular in patients with low exercise capacity [3], [8]. Accordingly, similarly to patients with heart failure [9], estimated peak VO2 or metabolic equivalent values do not necessarily have the same prognostic value as directly measured peak VO2 prior to cardiac rehabilitation, and data about the prognostic value of estimates of peak VO2 relying upon the maximal workload achieved in this context are sparse. Findings from a small study suggest that the maximal treadmill performance prior to cardiac rehabilitation may also be of prognostic value [10]. In many countries, cycle exercise testing is equally or even more popular than treadmill testing, and several differences exist between the two test modes [11], [12]. However, the prognostic value of the maximal cycle exercise workload prior to a rehabilitation program as well as changes in cycle exercise capacity during the rehabilitation program and cycle exercise capacity after rehabilitation, are not well characterized.

The aim of the present study was to assess the value of exercise testing parameters derived from the symptom-limited cycle exercise test for the prediction of all-cause and cardiovascular mortality in a large contemporary cohort of patients undergoing outpatient cardiac rehabilitation (OCR), the majority of whom had previous coronary revascularization.

Section snippets

Patients and follow-up

This is an observational study of patients entering a 12-week exercise-based comprehensive OCR program between March 1999 and June 2007 and undergoing a cycle ergometer exercise test prior to the start of the OCR activities. In December 2007, a follow-up of all 2199 consecutive patients was performed. Of these 2199 patients, 53 patients were excluded because we were unable to obtain follow-up information. Thus, the present analysis of predictors of outcome assessed at OCR entry is based on the

Study population and follow-up

The majority of the 2146 patients had CAD (93%). Eighty-six percent of the entire study population had undergone percutaneous coronary intervention, 24% coronary artery bypass grafting, and 15% valve surgery. After a median follow-up of 33 months (interquartile range 10–58) and 6519 patient years 74 patients had died. Forty-eight patients had died from cardiovascular causes (certain in 29, assumed in 19 cases), and 26 patients had died from other causes. Thus, annual all cause and

Discussion

The present study of a large cohort of patients confirmed an excellent long-term outcome after OCR during a median follow-up of almost three years. Nonetheless, maximal baseline bicycle workload was an independent predictor of all-cause and cardiovascular mortality, which is in agreement with previous studies on the prognostic value of peak VO2 and treadmill exercise capacity in this setting.

The present patient population consisted mainly of CAD patients with previous revascularization and

Acknowledgements

The authors of this manuscript have certified that they comply with the Principles of Ethical Publishing in the International Journal of Cardiology [26].

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    This study was supported by a grant of the Swiss Heart Foundation.

    1

    Dres. Di Valentino and Maeder contributed equally to this work.

    2

    Micha T. Maeder is supported by the Swiss National Science Foundation (Grant PBZHB-121007).

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